Fixed bug in statepoint.py for multiple generations per batch.
Fixed bug in statepoint.py for multiple generations per batch.

keadyk/openmc_mg_prepush,walshjon/openmc,shikhar413/openmc,johnnyliu27/openmc,samuelshaner/openmc,johnnyliu27/openmc,shikhar413/openmc,samuelshaner/openmc,samuelshaner/openmc,smharper/openmc,wbinventor/openmc,liangjg/openmc,amandalund/openmc,johnnyliu27/openmc,sxds/opemmc,mit-crpg/openmc,bhermanmit/openmc,keadyk/openmc_mg_prepush,bhermanmit/openmc,shikhar413/openmc,paulromano/openmc,keadyk/openmc_mg_prepush,kellyrowland/openmc,amandalund/openmc,paulromano/openmc,shenqicang/openmc,wbinventor/openmc,paulromano/openmc,kellyrowland/openmc,shenqicang/openmc,paulromano/openmc,smharper/openmc,lilulu/openmc,liangjg/openmc,lilulu/openmc,walshjon/openmc,liangjg/openmc,mit-crpg/openmc,amandalund/openmc,mit-crpg/openmc,liangjg/openmc,johnnyliu27/openmc,mjlong/openmc,amandalund/openmc,samuelshaner/openmc,nhorelik/openmc,sxds/opemmc,mit-crpg/openmc,walshjon/openmc,mjlong/openmc,wbinventor/openmc,shikhar413/openmc,smharper/openmc,smharper/openmc,wbinventor/openmc,bhermanmit/cdash,walshjon/openmc,nhorelik/openmc,lilulu/openmc